1. Field of the Invention
The present invention relates to an image forming apparatus and an image forming method, and more particularly to an image forming apparatus and an image forming method which form a color image by processing image signals read from a color document and using the processed signals.
2. Description of the Related Art
There is known an image forming apparatus, e.g., a digital color copying apparatus which reads a color image from a color document and copies the color document. In this digital color copying apparatus, a reading density of a line sensor which reads an image greatly affects the reproduced image quality. For example, in the case of reading a color image by a scanner using three color line sensors of red (R), green (G) and blue (B), a reading density of approximately 600 cpi is required in each line sensor in order to clearly reproduce a fine Ming-cho type character or prevent generation of moire in a dot document of approximately 175 cpi which is generally used for printed matter. When the reading density of the line sensor is increased in this manner, an image can be reproduced with high image quality.
On the other hand, when the reading density of the line sensor is increased, since the number of image signals or transfer speed of image signals is increased, a reference range is enlarged in signal processing to make reference to a surrounding of a target pixel, e.g., filter processing or segmentation processing, and the amount of calculation or number of delay memories is increased. Further, the reading density of the line sensor required for appropriately reproducing an image differs depending on a type of an image zone of the document to be copied.
Therefore, simply increasing the reading density increases the amount of calculation and hence leads to a reduction in copy speed, thereby increasing the cost of a circuit which executes image processing. As described above, in a color image forming apparatus, it is difficult to improve all of the image quality, the copy speed and the circuit cost when copying a document.